Head pose tracking typically involves periodically determining the location and orientation of a person's head within a space. The location of a person's head within a space is normally defined as a 3D location expressed in terms of a pre-established world coordinate system for the space. This location can, for example, be associated with the head centroid (i.e., the estimated center of the person's head). Although alternatively another readily ascertainable point associated with a person's head can be prescribed. Head pose orientation is usually defined in terms of rotation (pitch, roll, yaw) about three orthogonal axes having their common origin at the head centroid (or other prescribed head point). Typically, the pitch is the movement of the head up and down, the yaw is the movement of the head left and right, and the roll is the movement of the head from side to side.
Head pose is used in a variety of applications. For example, head pose is tracked in the context of an augmented reality application. In an augmented reality application, a user wears a goggle or similar device with at least one semi-transparent display so that the user can see both the real world and the virtual objects rendered onto the display. The virtual objects need to appear as if they were part of the real environment. One technical component in assuring that the virtual objects appear as if they are part of the environment is head pose tracking. When the user moves his or her head, the virtual objects, which are rendered on the display (that moves with the user's head), need to appear stationary with respect to the real environment.
One attempt at achieving accurate head pose tracking involves instrumenting the real environment, for example, by putting markers with known patterns at known locations of the wall or the ceiling. Images captured by a conventional video camera (which is mounted on a user's head or elsewhere in the space) are then processed using computer vision techniques to compute a user's head pose based on the location of the markers in the images. Another attempt involves the use of inertial sensors (e.g., gyroscopes, accelerometers, and a compass) that are mounted on the user's head (such as on a helmet or in a pair of goggles) to ascertain the user's head poses. In addition, head pose tracking schemes have been proposed where inertial sensors are combined with one or more conventional video cameras to obtain head pose estimates without having to instrument the environment.